Aluminum, a lightweight silvery-white metal, is one of the earth’s crust’s most plentiful metallic elements. This makes it the most extensively used non-ferrous metal, with typical applications ranging from marine and aerospace to construction and cookware. Aluminum holds its value down the supply chain because, according to the Aluminum Association, approximately 75% of all aluminum produced is still in good use to date since the aluminum corrosion resistance is excellent.
While this is a testament to aluminum’s recyclability and longevity, it’s susceptible to corrosion from acids, including alkalis, such as potassium hydroxide and sodium. This article answers the question, ‘Does aluminum rust?’ It also discusses different types of corrosion. Reach out to Minnesota Industrial Coatings for assistance with any aluminum corrosion issues.
Aluminum Corrosion: Does Aluminum Rust?
Aluminum doesn’t rust but is susceptible to corroding, which is the wearing away of metal. Corrosion refers to degeneration caused by environmental elements that happen naturally as nature attempts to return metals to their original state. Metal corrosion of any kind can significantly impact the functionality of a workpiece.
In extreme cases, rust (iron oxide) can cause structural damage like stress fractures and complete material failure. The degree and severity of aluminum corrosion have to be under the right conditions and stretch over weeks, months, or years. For example, while aluminum is a passive material, it’s a reactive metal by nature. It will react with water and bond with oxygen in the environment.
The result is a compound that forms a non-reactive oxide layer on the surface to protect the material underneath from further corrosion. Similar to stainless steel, the layer adheres well to the aluminum surface and does not flake off easily. What’s unique about aluminum is that there are several corrosion pathways. Understanding these multiple types of deterioration can help you apply relevant control measures that mitigate or reduce their occurrence.
Different Types of Aluminum Corrosion
Aluminum and its alloys have excellent corrosion resistance. In fact, commercially pure or non-heat treatable (1xxx) aluminum has the best corrosion resistance. Still, that quality is compromised by adding iron, copper, magnesium, or zinc alloys.
The decomposition of aluminum molecules into oxides that degrades their chemical and physical properties is known as corrosion or corrosive attack. The top three common types of corrosion include;
Atmospheric Corrosion
This is the most common form of corrosion that makes up the total damage caused to the material and occurs due to exposure to natural elements. Depending on the moisture content levels in the environment, atmospheric corrosion falls into dry, wet, and damp subcategories.
The concentration and variety of pollutants in the air, including environmental factors such as wind direction, temperature, and closeness to large water bodies, play a significant role.Â
Because the moisture content can change based on geographical location, some areas will observe more significant atmospheric corrosion than others. Design flaws that do not allow for moisture drainage and create pockets of condensation can also exacerbate aluminum corrosion.
Galvanic Corrosion
How a metal reacts depends upon its proximity to other metals to create an electrochemical series. Also known as dissimilar metal corrosion, galvanic corrosion affects aluminum when it is physically near a noble metal with lesser reactivity than aluminum.
The corrosion severity and intensity are highest when the two metals meet to form a galvanic cell. For example, if brass and aluminum are in contact and placed in seawater, the aluminum part that acts as the positive terminal (anode) will corrode.
This electrochemical series can materialize, particularly in boats where brass fittings are close to aluminum and are immersed in seawater to create a galvanic cell.
Pitting Corrosion
Pitting corrosion is characterized by small holes (pits) on the aluminum surface. Although salt should be present in damp conditions for pitting corrosion, the worst type of decay occurs in the presence of alkaline and acidic salts.
When the protective coating is physically damaged, it forms a weak point where corrosive substances attack the aluminum workpiece. Pitting corrosion is difficult to detect, which is why it can be the most dangerous form of erosion. The adjacent material will appear unaffected. If left unchecked, it penetrates and rapidly attacks with negative consequences.
Solutions to Aluminum Corrosion
With aluminums’ numerous applications ranging from airplanes and automobiles to elevators and electrical appliances, corrosion can’t be allowed to fester as it may have detrimental consequences. Aluminum corrosion and pitting removal can be costly, time-consuming, and tool-intensive.
To prevent corrosion, consider applying one of the following protective coatings that are appropriate for aluminum;
- Powder coating is a polyester-based coating whose dry polyester microbeads help create a protective barrier, safeguarding the aluminum against corrosion.
- Paint with high electrical resistance, especially if you’re worried about the risk of galvanic corrosion.
- Anodizing is an electrochemical process that works by immersing a metal part into an acid electrolyte bath to give the workpiece a durable and attractive anodic oxide finish.
The Bottomline
Suppose you deal with metal products and components or manufacture outdoor equipment. In that case, you need them to withstand one chemical reaction or the other, as well as the outside elements they encounter.Â
Powder coatings from Minnesota Industrial Coatings offer a cost-effective solution when you require a resilient finish that boosts your products’ quality and longevity. Contact Minnesota Industrial Coatings for more information.
